Critical theories are not the only lenses through which readers can interpret literature; however, they do provide firm foundations upon which readers can base their interpretations and analysis.  One of the defining elements of "great" literature is the extent to which the text provides a multitude of interpretations and perspectives.  For example, F. Scott Fitzgerald's The Great Gatsby provides the reader with complex characters in a complex situation that may be viewed from a variety of perspectives.  In Critical Theory Today, Lois Tyson uses The Great Gatsby as the primary text in her exploration of twelve literary theories.  In each chapter, Tyson defines the tenets of a different literary theory, discusses how the theory may be applied to literature overall, and then writes a literary analysis essay using the theory to interpret The Great Gatsby.  Tyson's work is "user-friendly" and provides her readers with clear definitions and detailed analysis.